This is what I use for 3D decoupage (if I’m not using foam pads for speed of drying) but it only comes in 80ml tubes so probably not what you want (I use it instead of silicone as there is very little smell with it)
http://www.pinflair.co.uk/adhesives-and-tools/adhesives/pinflair-glue-gel-kit
I don’t see why coating the back of your decoupage with PVA wouldn’t work it is certainly worth a try but you would need to leave it to dry before layering so it might take up a lot of space.
